Only one symbol must be included in every circuit diagram. What symbol is it?

Question 1 options:

a symbol for an anmeter

a symbol for a voltmeter

a symbol for a battery or some other voltage source

a symbol for a switch

A symbol for a battery.

Explanation:

A battery, because every sinlge circuit AC or DC must have a source of energy, to supply it to every single device that is part of the circuit.

The voltage is defined by the Ohm's law and it is equal to the product of the current by the resistance.